[ci] Make deploys fail if the spec build fails (#9)

Our CI deploy action currently asks a server at api.csswg.org to build
the spec, and then uses the response to that request as the build
output. However, it does not check that the response's HTTP status
code is successful, which can result in Internal Server Errors in that
server being "propagated" to this spec, rather than resulting in a
failed build. Similarly, fatal errors in building the spec (for
invalid Bikeshed syntax, for example) would result in the list of
errors being deployed.

This PR fixes that by allowing `curl` to fail for non-successful HTTP
status codes.

.github/workflows/deploy.yml

@@ -16,7 +16,7 @@ jobs:
       - name: Build spec
         run: |
           mkdir -p out
-          curl --retry 2 https://api.csswg.org/bikeshed/ --output out/index.html --header "Accept: text/plain, text/html" -F die-on=fatal -F file=@"index.bs"
+          curl --retry 2 --fail https://api.csswg.org/bikeshed/ --output out/index.html --header "Accept: text/plain, text/html" -F die-on=fatal -F file=@"index.bs"
 
       - name: Upload to Deno Deploy
         uses: denoland/deployctl@v1